1. Field of the Invention
The present invention relates to a spiral blade type fluid compressor for compressing a fluid such as a coolant gas in a refrigerating cycle.
2. Description of the Prior Art
Compressors are usually classified into a reciprocation type and a rotary type. In addition to these two types, there is a spiral blade type compressor, which successively moves a coolant from the suction side of a cylinder toward the discharge side thereof through work chambers to compress the coolant, and discharges the compressed coolant outside.
Such a conventional spiral blade type compressor will be explained with reference to FIG. 1.
The compressor has drive means 105 including a stator 101 and a rotor 103. The drive means 105 turns a cylinder 107. The cylinder incorporates a piston 111. The piston 111 is eccentric to the cylinder 107 by a distance of e, so that the piston 111 may rotate relative to the cylinder 107 through an oldham ring 109.
A spiral groove 113 is formed around the periphery of the piston 111 substantially over the whole length of the piston 111. A blade 115 is movably fitted in the groove 113. The periphery of the blade 115 is in contact with the inner face of the cylinder 107.
The blade 115 fitted to the spiral groove 113 defines a plurality of work chambers 117 in a space between the piston 111 and the cylinder 107. The volume of each work chamber 117 is determined by a corresponding pitch of the spiral groove 113. The pitches of the groove 113 gradually shorten from the suction side of the piston 111 toward the discharge side thereof. Namely, the volumes of the work chambers 117 defined by the blade 115 gradually decrease from the suction side (the right-hand side in the figure) toward the discharge side (the left-hand side in the figure), so that the coolant is gradually compressed while being conveyed from the suction side toward the discharge side.
The blade 115 moves inwardly and outwardly in the spiral groove 113, so that the periphery of the blade 115 is partly in contact with the inner face of the cylinder 107, to seal the work chambers 117.
Discharge capacity of the compressor is determined by the volume of the work chamber 117 defined at the suction side. To increase a refrigerant, a pitch of the blade 115 for the work chamber at the suction side must be extended.
FIG. 2 shows the blade 115. Compared with a small pitch region (the left-hand side in the figure) of the blade 115, a large pitch region (the right-hand side in the figure) involves large twists 119, which may be strongly pressed against the wall of the spiral groove 113. Contact pressure between the twists 119 and the groove 113 produces sliding resistance that prevents smooth movements of the blade 115 in the groove 113. If the blade 115 does not smoothly move in the groove 113, the periphery of the blade 115 will not be in tight contact with the inner face of the cylinder 107. This will break the sealed state of the work chambers 117 and deteriorate the discharge capacity.